This is something that has been bugging me for a while. When I first started doing book reviews, any time I received a book for review (whether it was from an author, publisher -whatever) I enclosed a thank you to them in the review. Something along the lines of "Special thanks to Author-Person for providing a free copy for review" at the end of the review after the rating. If they had a website I'd also give 'em a plug. I was told that looked tacky so I stopped.
I might get a handful of books from authors and publishers every other month or so, so I never really gave it much thought. But over the past month I've been receiving a lot of free books to review from a number of authors, publishers, and book groups. Now I feel kind of ungrateful by not mentioning them.
My question is this: Do you feel a "thank you" is necessary (or at least a mention) that you received the book in question for free and if so how? Does it make the review look tacky, devalue it, or make you look like a braggart? Those were actually some of the comments I once received, hence why I stopped.